Process for preparing a reforming catalyst comprising a support, a group viiib metal and a group viib metal

In this text, the groups for the chemical elements are given by the CAS classification described in the CRC Handbook of Chemistry and Physics, published by CRC Press, Editor-in-chief D R Lide, 81^st edition, 2000-2001.

The invention relates to a method for preparing reforming catalysts. There are two major categories of reforming catalyst. Firstly, catalysts for fixed beds generally comprise platinum and rhenium. Secondly, catalysts for moving beds generally comprise platinum and tin.

Catalysts for fixed beds which generally comprise platinum and rhenium are very stable over time and are regenerated every 3 to 24 months. However, their hydrogenolysation activity is too high at the start of each catalytic cycle. This unwanted activity can be reduced by adding sulphur at the end of the reforming catalyst preparation or at the start of the catalytic cycle. The sulphur is generally introduced in a reducing atmosphere by means of H₂S. However, the toxicity of H₂S renders it difficult to use. The use of sulphur-containing compounds of the polysulphide type has also been described. This sulphurization step is, however, independent of the other catalyst preparation steps.

The present invention pertains to a process for sulphurization using reducing agents for the formation of coordination complexes of a group VIIB metal, in particular rhenium. The C₅+ yields and reformate yields in particular are improved. Further, preparation of the catalyst is simplified since the sulphurization step is no longer independent but integrated into an impregnation step. Finally, using complexing agents can reduce the quantity of hydrochloric acid employed in the preparation.

Adding sulphur at the same time as rhenium in order to prepare a platinum-rhenium catalyst has been described in U.S. Pat. No. 4,246,095 which describes the use of an organometallic complex. That patent describes the use of a rhenium-carbonyl component containing sulphur.

U.S. Pat. No. 3,972,829 describes the preparation of a catalyst comprising at least platinum and optionally comprising rhenium via complexing agents. The complexing agents used are organic sulphur-containing acids, such as thio-acids and thiocarboxylic acids.

The preparation process of the invention is distinguished by the use of reducing agents to form coordination complexes of the group VIIB metal, in particular rhenium.

The invention concerns a process for preparing a reforming catalyst comprising a support, a group VIIIB metal and a group VIIB metal, and the resultant catalyst said process comprising the following steps in the order a) then b) or b) then a):

• • a step a) for impregnating the support with an aqueous solution of hydrochloric acid comprising a group VIIIB metal;
  • a step b) for impregnating the support with an aqueous solution comprising a group VIIB metal and a sulphur-containing complexing agent in a reducing environment, or a step b) for impregnation with an aqueous solution comprising a group VIIB metal, then with a solution comprising a sulphur-containing complexing agent in a reducing environment.

The reducing environment is selected from the group constituted by reducing atmospheres comprising more than 0.1% by weight of a reducing gas or a mixture of reducing gases, using reducing solutions comprising, with respect to the group VIIB metal, in the range 0.1 to 20 equivalents of reducing metals, reducing organic compounds or inorganic reducing compounds.